Fluorescent bands in massive corals result from terrestrial fulvic acid inputs to nearshore zone

Abstract

The discovery of yellow-green fluorescent bands in the skeletons of massive corals from inshore waters of the Great Barrier Reef, and the temporal and spatial correlations of these bands with adjacent river flow¹, prompted an investigation into the substances responsible for the phenomenon. We have determined that all regions of the coral skeleton contain fulvic acids^2,3 which impart a blue background fluorescence. The yellow-green fluorescent bands found only in inshore coral appear to result from enhanced concentrations of low-relative molecular mass (<10,000) fulvic acids from adjacent river input. These compounds are ubiquitous, and the yellow-green banding phenomenon can be expected to occur in massive corals located near to significant river systems. In the widely distributed genus Porites⁴, the great age of the largest colonies¹ means that extremely long, highly resolvable records of coastal runoff exist throughout tropical nearshore seas.